def conversionToPostOrder(self, inOrdErexpr):
"""
后序转换
"""
# 构建运算符优先级字典
prec = {"*": 3, "/": 3, "+": 2, "-": 2, "(": 1, ")": 1}
if not self.parseChecker(inOrdErexpr):
raise ValueError
opStack = Stack()
postOrderList = list()
exprList = inOrdErexpr.split()
for ch in exprList:
if ch.isdigit():
postOrderList.append(ch)
elif ch == "(":
opStack.push(ch)
elif ch == ")":
topOper = opStack.pop()
while topOper != "(":
postOrderList.append(topOper)
topOper = opStack.pop()
else:
# 比较运算符优先级，如果栈中运算符的优先级>当前运算符， 追加至转换列表中
while (not opStack.isEmpty()) and (prec[opStack.peek()] >
prec[ch]):
postOrderList.append(opStack.pop())
opStack.push(ch)
# 将栈中的运算符追加至转换列表中
while not opStack.isEmpty():
postOrderList.append(opStack.pop())
return "".join(postOrderList)
def parseChecker(self, symbolStr):
s = Stack()
balanced = True
index = 0
while index < len(symbolStr) and balanced:
symbol = symbolStr[index]
if symbol in "{[(":
s.push(symbol)
elif s.isEmpty():
balanced = False
else:
topSym = s.pop()
if not self.matches(topSym, symbol):
balanced = False
index += 1
if balanced and s.isEmpty():
return True
else:
return False